1. Field of the Invention
The present invention relates to apparatus and methods for regulating feedback related to hearing aid output stages. More particularly, this invention relates to regulating feedback related to hearing aid output stages in hearing aids having feedback cancellation processing.
2. Description of the Prior Art
In order to save complexity and power in a digital signal processing hearing aid, it is valuable to use a direct digital to class D output stage. Power dissipation is low, and no analog circuitry is required. A problem arises with this configuration, due to the fact that the gain of the output stage varies with the voltage of the battery used to power it. The battery voltage depresses when a loud signal is processed by the hearing aid, for example.
In hearing aids incorporating feedback cancellation, the feedback cancellation algorithm attempts to model the acoustic feedback path, including the effects of the hearing aid amplifier, receiver, and microphone as well as the vent acoustics. Thus, the feedback cancellation algorithm attempts to match the gain of the output amplifier, which varies with the voltage of the battery.
A need remains in the art for apparatus and methods for regulating the voltage to the output stage of the amplifier, in order to regulate feedback effects of variation in gain caused by voltage variations.